JPH0714389B2 - Nuclear magnetic resonance imaging apparatus and other interface method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radio frequency interface circuit. More specifically, the present invention relates to a nuclear magnetic resonance imaging apparatus particularly applied to an interface between transmission and reception of a magnetic resonance spectroscopic probe signal, and another interface method and apparatus. The method and apparatus find application in magnetic resonance imaging and magnetic resonance scientific or physical analysis, as well as in other applications where the same coil is alternately actuated as a radio frequency transmit and receive antenna. .

The magnetic resonance spectrometer has a linear RF
(Radio frequency) polarization has been commonly used, where significant gain could be obtained by utilizing quadrature coils. Conventionally, a magnetic resonance spectrometer utilizing the quadrature coil is generally provided with a radio frequency signal source having two signal components offset by 90 degrees, but in order to achieve this phase shift, radio frequency transmission is performed. Machines and signal separators are commonly used. The two radio frequency signal components are sent to a pair of quadrature probes via a parallel circuit and a parallel matching network. The quadrature probe is connected to the parallel receive path. The receiving path can be provided with a quarter-wave line and a diode terminal, respectively, or other means acting as a double throw switch for switching between transmitting and receiving. In addition, each parallel path can include preamplifiers, rectifiers, analog-to-digital converters, and other receivers and signal processors.

The drawback of the prior art is that it has a wide range of signal strengths, e.g.
The inability to maintain signal integrity over the dBRF envelope. The prior art devices are also susceptible to distortion of the pulse waveform, relative amplitude modification, clipping of the waveform portion, or loss of the entire signal portion, which tends to cause distortion in the low level portion of the envelope.

Another issue is the isolated imperfections of the transceiver. The transmitter causes degradation of the received signal and increases the noise level of the radio frequency signal. This increase in noise is due to noise spilling from the transmitter to the receiver or loading of the probe output by the transmitter.

Further, there is a problem of selecting a member that can sufficiently operate even in the vicinity of a high magnetic field. Hybrid transformers, ferrite core transformers, or other transformers incorporating highly permeable materials, saturate at high magnetic fields associated with magnetic resonance imaging, but the transformers are well spaced from the magnetic field. By doing so, the additional signal on the transmission line is reduced and the phase can be shifted.
Further, the substitution of the air-core hybrid transformer complicates the electronic circuit configuration and easily deteriorates the performance.

The present invention provides a novel nuclear magnetic resonance imaging apparatus that solves the above and other problems and achieves improved magnetic resonance imaging and spectroscopy, and other interface methods and apparatus.

SUMMARY OF THE INVENTION According to the present invention, a magnetic resonance spectrometer and a radio frequency (R
F) An interface device for interfacing a probe is provided. The first RF switching means selectively allows or blocks passage of radio frequency signals. The first RF switching means is operatively connected to the first probe port and also to a radio frequency transmitter. Phase shifting means for shifting the radio frequency signal is operatively connected between the first RF switching means and the second probe port. Second RF switching means operatively connected to the second probe port for selectively permitting or blocking the passage of radio frequency signals,
It is designed to connect to a receiver. The first and second RF switching means are actuated by the control means and one of the
RF switching means allow the passage of radio frequency signals, while the other
The RF switching means is adapted to block the passage of radio frequency signals.

According to a more limited feature of the invention, the third RF switching means selectively switches between the transmitter and the first RF switching means. That is, between the transmitter and the first RF switching means, when the first RF switching means permits the passage of the radio frequency signal, the band filter means is switched to, and the first RF switching means is switched to the radio frequency. If the signal is blocked, the band stop filter is switched to.

According to another feature of the present invention, an interface device is provided. The first PIN diode has an anode operably connectable to the radio frequency transmitter and a cathode operably connected to the first port. A first quarter-wave line operatively connects the first port to a second port, and a second quarter-wave line connects the second port to the second port.
Is connected to the anode of the second PIN diode.
The cathode of the second PIN diode is operatively connected to ground. The second quarter-wave line can be operably connected to a radio frequency receiver.

According to a further limiting feature of the invention, the interface device is incorporated into a magnetic resonance imaging device.
The imaging device is provided with means for forming a main magnetic field and means for forming a magnetic field gradient across the main magnetic field. A transmitter selectively sends the magnetic resonance excitation signal to an interface device for transmission to a quadrature probe connected to the first and second ports. A magnetic resonance spectrometer receiver is selectively switched into connection with the port to receive the signal from the quadrature probe. An image of the sample subjected to the magnetic resonance examination is reconstructed from the received signal by the image reconstructing means and displayed on a suitable image display means.

According to another feature of the present invention, an interface method is provided. Passage of radio frequency signals to the first and second ports is selectively enabled or blocked. The phase of the signal is shifted by a preselected phase angle between the first and second ports. During transmission, the signal at the first port leads the signal at the second port by a preselected phase angle, while during reception the radio frequency signal received at the first port is at a preselected phase angle. Only lags the radio frequency signal received at the second port. Radio frequency signals sent from the port to the receiver are selectively allowed or blocked from passing. More specifically, the passage of the transmitted radio frequency signal to the port is permitted when the passage of the received radio frequency signal to the receiver is blocked, and the passage of the received radio frequency signal to the receiver. Is allowed when the transmitted radio frequency signal is blocked from passing from the transmitter.

A first advantage of the present invention is that it provides excellent pulse fidelity over a wide range of signal strengths.

An advantage of the present invention is that the isolation between transmission and reception is improved.

Another advantage of the present invention is that more sharp and detailed magnetic resonance images are easily reconstructed.

An advantage of the present invention is also that it is easy to configure, test, and implement.

While the following is a detailed description of the preferred embodiments of the present invention, further advantages will become apparent to those skilled in the art upon reviewing the above detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings are described below. It should be noted that the drawings are merely for showing preferred embodiments of the present invention and do not limit the present invention.

FIG. 1 is a schematic diagram of a magnetic resonance imaging apparatus.

FIG. 2 is a circuit diagram of the magnetic resonance imaging apparatus and other interface apparatus according to the present invention.

FIG. 3 shows the same circuit when the interface device is in its transmission mode.

FIG. 4 shows the same circuit when the interface device is in its receive mode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The magnetic resonance imaging apparatus shown in FIG. 1 is provided with means A for generating a main magnetic field, by means of which a strong longitudinal magnetic field is generated over the image (map) area. It A plurality of superconducting magnets are arranged in the periphery, and a generally cylindrical image area is formed therein. A magnetic field gradient is selectively generated in the main magnetic field by the gradient coil means B, and the position is encoded. The radio frequency magnetic resonance excitation signal is passed by the magnetic resonance excitation transmitter C through an interface device D and a probe E, for example a quadrature component coil.
Selectively sent to. The probe E receives a magnetic resonance signal obtained from a sample in the image area during the resonance excitation transmission signal or pulse. The received signal is sent to the receiver F by the interface device D. For the interface device D,
Further details are provided below in connection with FIG. The main magnetic field generating coil A, the gradient coil B, the transmitter C, the interface device D, and the receiver F are controlled by a control computer G to generate appropriate reconstruction data. The received radio frequency signal is reconstructed by a conventional imaging device H into electronic data that indicates the density, location, and other characteristics of the resonant nuclei within the image area. An image is then synthesized from the received nuclear data and displayed by a conventional monitoring device or other display means I.

FIG. 2 shows a circuit configuration of the interface means D according to the present invention. The means D is provided with the first RF switching means 10 and the radio signal transmitted from the transmitter C is transmitted. Selectively allow or block the passage of frequency signals. In the first RF switching means in this embodiment,
A first PIN diode 12 is provided which is selectively biased between conducting and non-conducting. The first PIN diode is a DC blocking capacitor 1
Transmitter C via 4 and 50 ohm cable 16
Has an anode connected to. Desirably, the first PIN
A half-wave cable 18 is connected to the cathode of the diode so that the diode is positioned further away from the probe E.

The received radio frequency signal is selectively phased by the phase shifting means 20 by a preselected phase angle-in this embodiment 90 degrees. The phase shifting means 20 is connected to the end of the half-wave cable 18 on the side opposite to the first PIN diode 12. Further, in this embodiment, a quarter wavelength cable is used as the phase shifting means.

A first port 30 interconnecting with one of the quadrature coils E is connected to the first RF switching means 10 and the phase shifting means 20 by a first 100 ohm coaxial cable 32. The second port 34 is connected to the other end of the phase shifting means 20 by a 100 ohm cable 36 of the same length as the first 100 ohm cable 32. By positioning the phase shifting means 20 between the two ports, the signal at the first port leads the signal at the second port during transmission by the selected phase angle. In the receive mode, the phase shifting means causes the signal from the first port to lag the signal from the second port by the selected phase angle.

The second RF switching means 40 selectively permits or blocks passage of radio frequency signals from the ports 30 and 34. That is, the signal is sent to the receiver F in the reception mode, and the passage of the signal is blocked in the transmission mode. In this embodiment, the quarter-wave cable 42 is used as the second RF switching means. The cable 42 extends from the phase shifting means 20 adjacent to the second port 34 to the anode of the second PIN diode 44. The quarter-wave cable images the impedance of the phase shifting means termination to its PIN diode termination. When the second PIN diode is gated and conducting, the quarter wave cable is open circuit, and when the second PIN diode 44 is gated and non-conducting,
The quarter wave cable 42 operates as a 50 ohm matched transmission line. The second RF switching means 40 is connected to the receiver F by a DC blocking capacitor 46 and a 50 ohm coaxial cable 48.

Filter means 50 improves the quality of the signal in both transmit and receive modes. The filter means is provided with a third RF switching means 52, for example a third PIN diode, which selectively switches the connection with the transmitter. That is, a bandpass filter is connected to the transmitter in the transmission mode and a bandstop filter is connected to the transmitter in the reception mode. More specifically, a quarter-wave cable 54 is connected between the anode of the first PIN diode 12 and the anode of the third PIN diode 52, and the cathode of the third PIN diode is a resistor 56. It is also connected to ground via a DC blocking capacitor 58. When the third PIN diode is gated and conductive, the quarter wave cable 54 connects to ground, thereby creating an open circuit to the transmitter at the operating frequency and acting as a bandpass filter.

A fourth quarter-wave cable 60 and a DC blocking capacitor 62 are connected between the third quarter-wave cable 54 and ground, and when the third PIN diode 52 is gated and becomes non-conducting. , The third and fourth quarter-wave cables operate as half-wave cables. This effective half-wave cable extends from the anode of the first PIN diode through a DC blocking capacitor 62 to ground to form a bandstop filter. That is, the radio frequency signal from the transmitter is shorted to ground.

To put the interface device D into the transmission mode, a DC bias voltage is applied to all PIN diodes by the control means G to bias the diodes to make them conductive.
This bias voltage is applied to the connection point between the fourth quarter-wave cable 60 and the DC blocking capacitor 62 through the resistor 70 and the radio frequency chain device 72. When the DC bias is removed, the PIN diode is gated and becomes non-conducting, putting the interface device D in receive mode.

Next, please refer to FIG. 3 together with FIG. In transmit mode, a DC bias is applied and all PIN diodes are forward biased into the very low radio frequency impedance region. The value of resistor 56 is selected so that all diodes are properly biased by the applied bias potential. The third PIN diode 52 shorts the third quarter-wave cable 54 to ground so that the cable is open circuited. That is, the filter 50 operates as a band filter. The half-wave cable 18 operates as a 50 ohm matched transmission line from the transmitter C to the connection point between the first probe cable 32 and the 90 degree phase shifting means 20. The first port 30 is driven 90 degrees ahead of the second port 34. The second quarter-wave cable 42 forms a circuit at the connection point between the phase shifting means 20 and the second port cable 36, because the second PIN diode 44 is almost a short circuit. Is. This protects the receiver F from the power of the transmitted radio frequency signal.

Further, please refer to FIG. 4 together with FIG. In receive mode, the negative voltage biases all PIN diodes to a very high radio frequency impedance. The third and fourth quarter-wave lines 54,60 become half-wave lines and form an effective radio frequency short circuit at the output of the transmitter. First
The PIN diode 12 is substantially opened to prevent a signal from flowing between the transmitter and the receiver. The first quarter wave cable 20 delays the signal from the first port 30 by 90 degrees before the signals from the first and second ports are combined. The second quarter wave cable 42 acts as a 50 ohm matched transmission line from probe E to receiver F. The second PIN diode 44 is almost open circuit.

Although the present invention has been described with reference to a preferred embodiment particularly applied to a nuclear magnetic resonance imaging apparatus, it will be apparent to those skilled in the art from the above detailed description that the present invention can be modified and changed. I understand. The invention includes all such modifications and alterations insofar as they come within the scope of the appended claims.

Claims (20)

[Claims] 1. An interface device for a nuclear magnetic resonance imaging device for reconstructing a visible image inside a sample, said device comprising a main magnetic field generating means for forming a strong and uniform main magnetic field in an image region, Gradient magnetic field generating means for forming a gradient magnetic field in the main magnetic field of the image area, a radio frequency transmitter for selectively transmitting a magnetic excitation signal, and a passage from the radio frequency signal transmitter to the first probe selectively. First RF switching means for permitting and blocking, and phase shifting means operatively connected between the first probe and the second probe for phase shifting the radio frequency signal by a selected phase angle. Second RF switching means operatively connected to the second probe and radio frequency receiver for selectively permitting and blocking passage of the radio frequency signal, and selectively the first RF switching means. Gate and lead And the second RF switching means is selectively gated to be non-conductive to achieve a transmission mode and the first RF switching means is selectively gated to be non-conductive, and the second A control means for selectively gated the RF switching means to make it conductive to achieve a reception mode and a signal operatively connected to the receiver for displaying an image of an internal area of an object in the image area are displayed. An image reconstruction means for generating, and operatively connected with said image reconstruction means,
An interface device for nuclear magnetic resonance imaging apparatus and the like, further comprising display means for performing visible display by the image display signal. 2. A device according to claim 1, wherein said device comprises third RF switching means for selectively connecting a band filter in the transmit mode and a band stop filter in the receive mode to the transmitter. The nuclear magnetic resonance imaging apparatus and other interface apparatus characterized by further comprising. 3. A nuclear magnetic resonance imaging apparatus for interfacing a magnetic resonance spectrometer and a probe, and an interface apparatus for other uses, wherein the apparatus is operatively connected to a first probe port and a magnetic resonance spectrometer transmitter. A first RF switching means for selectively permitting and blocking the passage of radio frequency signals, and operatively connected between the first probe port and the second probe port, Phase shifting means for shifting the radio frequency signal by a selected phase angle and the second probe port are operatively connected to the magnetic resonance spectrometer receiver so as to connect the radio frequency signal. Second RF switching means for selectively permitting and blocking passage, and said first and second RF
The switching means is selectively controlled such that when one RF switching means permits passage of a radio frequency signal, the other RF switching means prevents passage of the radio frequency signal, and thus the first Magnetic resonance reception when the magnetic resonance transmitter is transmitting the radio frequency signal to the probe port such that the radio frequency signal at the first port leads the radio frequency signal at the second port by a selected phase angle. Is isolated from the probe port, and the magnetic resonance receiver delays the radio frequency signal from the first port from the radio frequency signal from the second port by a selected phase angle. The magnetic resonance transmitter comprises a control means isolated from the probe port when receiving a radio frequency signal from the port. Nuclear magnetic resonance imaging device, other interface device. 4. The apparatus of claim 3, wherein said apparatus further comprises filter means operatively connected to said first RF switching means for filtering radio frequency signals. The above-mentioned nuclear magnetic resonance imaging apparatus and other interface apparatus. 5. A device according to claim 3, wherein said device selectively switches said first RF switching means, said first RF switching means permitting passage of radio frequency signals. And a third RF switching means for connecting the band filter to the first RF switching means when the first RF switching means is blocking the passage of radio frequency signals. The above-mentioned nuclear magnetic resonance imaging apparatus and other interface apparatus. 6. A nuclear magnetic resonance imaging apparatus according to claim 3, wherein the first and second RF switching means are provided with PIN diodes. Interface device. 7. An apparatus according to claim 3, wherein said phase shifting means carries out a 90 degree phase shift. 8. The apparatus according to claim 7, wherein the phase shifting means is a quarter-wave cable, and the nuclear magnetic resonance imaging apparatus and other interface apparatus. 9. The apparatus of claim 3, wherein the first RF switching means is an anode operatively connected to the transmitter and a cathode operably connected to the first port. A phase-shifting means having a quarter-wave cable operably connected between the first and second ports, and the second RF switching means being One end of which is operatively connected to the first quarter-wave cable and the other end of which is operatively connected to an anode of a second PIN diode for coupling with the receiver, An interface device for a nuclear magnetic resonance imaging apparatus and the like, characterized in that the cathode of the second PIN diode is provided with a second quarter-wave cable operatively connected to ground. 10. The apparatus of claim 10, further comprising a PIN diode selectively switching one of the bandpass filter and the bandstop filter to connect with the transmitter. The nuclear magnetic resonance imaging apparatus and other interface apparatus characterized by the above. 11. The apparatus according to claim 10, wherein the band filter comprises the first RF switching means and the PI.
The nuclear magnetic resonance imaging apparatus and other interface apparatus characterized by comprising a quarter wavelength cable operatively connected to the anode of the N diode. 12. The apparatus of claim 11 wherein said bandstop filter comprises another quarter wave cable operatively connected between the positive pole of said PIN diode and ground. The nuclear magnetic resonance imaging apparatus and other interface apparatus characterized by the above. 13. A nuclear magnetic resonance imaging apparatus, and other interface apparatus for use with an anode operably connected to a radio frequency transmitter and a cathode operably connected to a first port. A first PIN diode having a first quarter-wave cable operatively connected between the first and second ports, a cathode operatively connected to ground and a radio frequency receiver A second quarter-wave cable operatively connected between the anode and a second port of a second PIN diode having an anode operably connected to the machine. The nuclear magnetic resonance imaging apparatus and other interface apparatus characterized by the above. 14. The apparatus of claim 13, wherein the apparatus includes a third quarter-wave cable operably connected to an anode of the first PIN diode and the third quarter-wave cable. A third having an anode operably connected to the quarter-wave cable and a cathode operably connected to ground
The nuclear magnetic resonance imaging system further comprising a PIN diode and a fourth quarter-wave cable operatively connected between the third quarter-wave cable and ground. Equipment and other interface equipment. 15. The device according to claim 14, wherein the device selectively applies a DC bias to the first, second and third PIN diodes to cause the PIN diode to operate at a low radio frequency. Biasing to an impedance state so that the first PIN diode transmits a radio frequency signal to the first port and the second port receives the radio frequency signal delayed by 90 degrees to the first port. However, the second quarter-wave cable forms an open circuit, and the third quarter-wave cable further comprises biasing means for operating as a bandpass filter. The above-mentioned nuclear magnetic resonance imaging apparatus and other interface apparatus. 16. The device according to claim 15, wherein the biasing means comprises the first, second and third biasing means.
The PIN diode is selectively biased into a high radio frequency impedance state such that the first PIN diode blocks transmission of radio frequency signals therethrough and the radio frequency signal from the first port is coupled to the second radio frequency signal. 90 degrees behind the radio frequency signal from the port of said second quarter-wave cable through said first and second
Core for conducting a received radio frequency signal from a port of said and said third and fourth quarter-wave cables forming an effective half-wave cable which acts as a band stop filter. Magnetic resonance imaging equipment and other interface equipment. 17. A nuclear magnetic resonance imaging apparatus for interfacing a transmitter, a receiver, and a co-probe assembly having first and second leads, wherein the method is the probe. Selectively applying a radio frequency signal to the lead wire to form a transmit mode and selectively blocking passage of the radio frequency signal from the transmitter to the probe lead wire to form a receive mode. Permitting passage of a radio frequency signal received from a lead of the probe to the receiver in the reception mode and blocking passage of the radio frequency signal to the receiver in the transmission mode; and Phase shifting the radio frequency signal between the leads of the first and second probes by a selected phase angle and therefore transmitting Mode, the signal of one lead wire leads the signal of the other lead wire by the selected phase angle, and in the receiving mode, is delayed by the selected phase angle. A nuclear magnetic resonance imaging apparatus characterized by the above, and an interface method for others. 18. The method according to claim 17, wherein the method receives a radio frequency signal from the transmitter,
The nuclear magnetic resonance imaging apparatus and the other interface method, further comprising a step of selectively connecting to the band filter in the transmission mode and to the band elimination filter in the reception mode. 19. The nuclear magnetic resonance imaging apparatus and other interface methods according to claim 18, wherein the selected phase angle is 90 degrees. 20. The method of claim 18, wherein the method biases the PIN diode into a low radio frequency impedance state to form the transmission mode and causes the PIN diode to enter a high radio frequency impedance state. The nuclear magnetic resonance imaging apparatus and the interface method for others as described above, further comprising a step of biasing to the step of forming the reception mode.